Reduced profile wind tower system for land-based and offshore applications

ABSTRACT

A reduced profile wind tower system includes a slim cylindrical spinal core extending up vertically from a foundation. A turbine nacelle is mounted on a top end of the core. Wind turbine blades extend out from the nacelle. A plurality of axially loaded tubular arms, braced by the core, are spaced around the core and link to the core through continuous shear wings or discrete bracket assemblies. The tubular arms and shear wings extend up from said foundation. The tubular arms can be set either vertically or slightly sloped; cables may substitute for the tubular arms and a pontoon may substitute for an on ground foundation.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/584,717,filed Sep. 26, 2019, which '717 application is a continuation ofapplication Ser. No. 15/055,047, filed Feb. 26, 2016, now U.S. Pat. No.10,465,660 B2, dated Nov. 5, 2019, and Applicant claims priority under35 U.S.C. § 120 therefrom. This application claims benefit under 35U.S.C. § 119(e) of provisional patent application No. 62/127,497 filedMar. 3, 2015. The '727, '047 and '497 applications are incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates to tall wind turbine towers.

BACKGROUND OF THE INVENTION

There is a wide consensus that the world is moving toward a significantexpansion in wind power generation. According to the U.S. EnergyInformation Administration (EIA), in 2010 wind energy accounted forabout only 2% of the total electricity generated in the United States.Nonetheless, from the year 2000 to 2010, electricity generated from windin the U.S. increased more than fifteenfold. EIA reports that Americanwind power topped 4% of the total U.S. power capacity in 2013. Manybelieve that supplying 20% of our electricity from wind is within reachby 2030.

According to the U.S. Department of Energy, in order to harvest moreenergy at higher altitudes where wind velocity is higher, wind towersare becoming taller. At the same time, in order to cut unit costs, windturbines are gradually getting bigger and heavier and blades are gettinglonger. The Triangle Business Journal reported that “in 2000, windturbines reached 80 meters with blades rotating, and by 2012, rotatingblades reached heights of 130 meters. Allowing the height to grow beyond180 meters could be a game changer.” The following considerations,therefore, are essential:

A major component of wind power project costs is invested in thefabrication, transportation, and installation of the support structureand foundations. Reducing costs of the superstructure and foundationsystems, as well as facilitating the tower's installation andtransportation to the project site, is necessary in making wind powermore competitive with other sources of energy.

At the present time, the most common wind tower structure is atapered-tube construction: a conical tower of a large diameter. It is amassive and costly structure. With the trend towards taller towers,larger and heavier turbines and longer blades, the diameter of today'stower will keep getting larger and its total cost rising steeply. Itsfabrication, transportation, and erection costs will disproportionallyincrease, hindering the effectiveness of wind power installations andrendering the present tower structure less and less viable. Today, insome markets, wind is a competitive form of energy. The innovationproposed here resolves the shortcomings of today's tower and gives windpower a greater edge to become a mainstream energy resource in a widermarketplace.

According to a report by the United States Department of Energy (DOE)Plan for 2007-2012, taller wind turbine towers can access high velocitywinds because of wind shear (an increase in wind velocity as heightabove the ground increases). However, taller towers are more expensiveand more difficult to transport and erect. To support taller towers,turbine bases must normally grow in diameter. Bases that are more thanapproximately 4 meters in diameter cause transport costs to skyrocketbecause of limitations in road capacity, bridge heights, and utilityline heights.

All wind towers installed to date, whether a tapered tube or a taperinglattice structure, are essentially the same basic structural system: afree-standing vertical cantilever. Lattice tower structures have been inuse in transmission lines and antenna installations for many years. Somelattice towers, in one form or another, have been used in wind towerinstallations. At the present time, however, the most common wind towerstructure is the tapered tube, a conical tower of a large diameter. Itis a massive and costly structure. The base diameter of such a structurecan exceed 4 meters when it gets taller than approximately 80 meters.

Tower structures are subjected to static and dynamic forces, primarilyvertical forces, such as the self-weight of the tower, turbine, andblades, and to lateral forces, such as wind and seismic forces.Generally, however, the lateral forces drive the design of the windtowers. The lateral forces produce bending moments and sway the towerstructure. As the tower gets taller and the turbine gets larger andheavier, the magnitude of the bending moments and sway increaseconsiderably.

As today's free-standing tapered-tube tower structure becomesexcessively large, it becomes prohibitively expensive, hindering thecompetitiveness of wind power as an alternative source of energy,thereby rendering such a structural system less and less viable. Toprevent the costs of wind tower installations from spiraling out ofcontrol, there is a pressing need to reverse the limitations of thepresent tower system.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a simple,structurally potent and aesthetic wind turbine tower.

It is also an object to provide a wind turbine tower which is costeffective to manufacture, transport, and install.

It is also an object to provide a wind turbine tower which can reachheights and accommodate powerful winds at high altitudes.

It is also an object to provide a wind turbine tower which can be usedboth on land and offshore

SUMMARY OF THE INVENTION

The above features and objectives are achieved by utilizing a reducedprofile wind turbine tower (RPWTT) structure of the same footprint as apresent massive tapered-tube tower, but substituting instead a slimmeruniform cylindrical spinal core surrounded by a number of axially loadedtubular arms interacting with the tower core via shear wings. The armsare laterally braced by the spinal core utilizing bracing rings. Globalstability of the tower is achieved with the interconnected spinal core,shear wings, and tubular arms acting together.

A number of different embodiments are described based on the number oftubular arms used, types of bracing rings, open or closed shear wings orbrackets, and fanned-out or straight tubular arms.

Other embodiments relate to the substitution of cables for the tubulararms. The cables are post-tensioned so that they can resist both tensionand compression. Post-tensioning is a well-known technique commonly usedto strengthen concrete slabs and other structural systems and elementsin the construction of bridges, parking garages, and buildings.

Terrestrial RPWTT on foundations, as well as offshore RPWTT solutions onfloating platforms, are so described.

The reduced profile wind turbine tower design of the present inventionfundamentally changes the tower's structural behavior and opens newopportunities for taller, slimmer, more cost-effective wind towers thatare significantly easier and faster to fabricate, transport, andinstall. The reduced profile wind turbine tower of the present inventionhas unmatched versatility and design flexibility, making it adaptable tomany land-based and offshore applications. It permits efficient andeconomical super tall wind towers capable of harnessing more powerfulwinds at higher altitudes. The reduced profile wind turbine tower designpermits optimization of the entire wind power system to include thetower structure and foundations with the power generating system,thereby unlocking previously untapped potential for reducing totalexpenditures and lowering the unit cost of energy.

Significantly, the reduced profile wind turbine tower boosts the hubheight of today's typical wind tower without exceeding the currenttransportation limits. The new tower is virtually maintenance-free. Thereduced profile wind turbine tower is slimmer, lighter, and non-tapered.Handling the reduced profile wind turbine tower sections is considerablyeasier and can be accomplished in less time. Unlike conventional towers,the new tower stiffness can be increased as needed at relatively minimalcost to improve the tower performance and its structural response tomeet design needs. The reduced profile wind turbine tower can support aclimbing tower crane to erect the next tower level, as well asfacilitate the installation of the turbine and blades, therebycircumventing the need for a mammoth and costly land-staged crane.Furthermore, it addresses the tower connections, the critical link inany structure. Known proposed tall towers add numerous connections,thereby increasing many such critical links. With the reduced profilewind turbine tower, the number of connections is minimized and fieldsplicing is simplified.

Designing and building much taller towers than today's 80 m high windtowers is possible so long as they comply with the laws of physics thatnecessitate a more robust structural system. At the present time, allknown proposed tall towers translate “robust” structure to mean “largersize” structure. “Robust”, however, need not mean “larger size”. Thereduced profile wind turbine tower achieves a more “robust” structure byshrinking the tubular system of today's tower while boosting the tower'sstiffness and load resisting capacity by other, more efficient,structural means. In doing so, the reduced profile wind turbine towerreverses the limitations of today's tower and completely transforms thelatter's massive structural system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can best be understood in conjunction with theaccompanying drawings, in which:

FIG. 1 is a bending moment diagram for a prior art free-standing towercore subjected to lateral force P.

FIG. 2 is a cross-section view illustrating the basic towertransformation utilizing a square arrangement of tubular arms. The priorart tower cross-section 5 is shown in dashed lines for comparison. Thenew reduced profile wind turbine tower RPWTT 10 of the present inventionis shown with uniform spinal core 12, shear wings 16 and tubular arms14, which are shown in solid lines.

FIG. 3 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention showing a uniform spinal core 12,tubular arms 14, continuous shear wings 16 and disc-shaped bracing rings17. A wind turbine nacelle 22 with blade 24 and foundation 20 are alsoshown.

FIG. 4 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention showing the use of cone-shaped bracingrings 26.

FIG. 5 is a bending stress distribution of a prior art cylindrical ortapered-tube tower 5.

FIG. 6 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention showing openings 28 in the shear wingswith pairs of circular flange plates-18 at the edge of each opening.

FIG. 7 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention showing assemblies of rigid brackets32 with pairs of circular flange plates 18 and open areas 30 betweenassemblies.

FIG. 7A is an isometric view of the RPWTT of FIG. 7, shown with therigid brackets 32 and circular flange plates 18 being enclosed.

FIG. 8 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention using fanned-out tubular arms 34engaged with foundation 20 at the bottom with optional horizontal tubes36.

FIG. 9 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention employing post-tensioned cables 40 asa substitute for tubular arms 14; this embodiment also uses assembliesof rigid brackets 32 with pairs of circular flange plates 18 and openareas 30 between assemblies.

FIG. 10 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention employing post-tensioned cables 40connecting at the bottom to rock anchors 44 which go through thefoundation 42.

FIG. 11 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention employing post-tensioned cables 40which are preferably fanned out 48 at bottom around the foundation 46and terminate in rock anchors 44.

FIG. 12 is a tower cross-section showing a reduced profile wind turbinetower RPWTT 10 of the present invention with tubular arms orpost-tensioned cables 50 with wider distance from uniform spinal core 12beyond a typical prior art tower 5; tubular arms or cables 50 are shownin an extended-square arrangement.

FIG. 13 is a tower cross-section of a reduced profile wind turbine towerRPWTT 10 of the present invention utilizing a plurality of hexagonarrangement of six tubular arms or post-tensioned cables 50 attached bybrackets 32 to spinal core 12.

FIG. 14 is a vertical section of a reduced profile wind turbine towerRPWTT 10 of the present invention with tower height h. Rigid brackets 32with pairs of circular flange plates 18 are at two heights, ⅖ h from thebottom and ⅘ h from the bottom. Tower spinal core 12 and tubular arms orpost-tensioned cables 50 are subjected to lateral force P.

FIG. 15 is a bending moment diagram of the reduced profile wind turbinetower RPWTT 10 of the present invention configuration of FIG. 14, withrotational fixity at ⅖ h and ⅘ h from the bottom.

FIG. 16 is a vertical section of a floating reduced profile wind turbinetower RPWTT 10 of the present invention for offshore use. Fanned outpost-tensioned cables 48 are anchored in a submerged pontoon 52 which isheld below both high water level 56 and low water level 58 by tie-downcables 54 via anchorage 62 in seabed 60.

FIG. 16A is a vertical section of a floating wind turbine tower of priorart construction (either tapered tube or lattice type or hybridsthereof) 90, with new, optional fanned out base section 91, installed ona submerged pontoon, as is the reduced profile wind turbine tower RPWTT10 of FIG. 16.

FIG. 17 is a top view of a reduced profile wind turbine tower RPWTT 10of the present invention at the bracket level showing the detail of thefield connections between uniform spinal core 12, tubular arms 14, rigidbrackets 32 and top circular flange plate 70.

FIG. 18 is a vertical section of the reduced profile wind turbine towerRPWTT 10 of the present invention at bracket level showing the detailsof the field connections of FIG. 17 from a view point 90 degrees away.

FIG. 19 is a top view of the reduced profile wind turbine tower RPWTT 10of the present invention at the bracket level (comparable to FIG. 17)showing the detail of the field connections between uniform spinal core12, cable assemblies 86, rigid brackets 32, and top circular flangeplate 76.

FIG. 20 is a vertical section of the reduced profile wind turbine towerRPWTT 10 of the present invention at bracket level of the fieldconnections of FIG. 19 from a view point 90 degrees away.

LIST OF REFERENCE NUMERALS

-   5 prior art tapered-tube tower.-   10 reduced profile wind turbine tower (RPWTT)-   12 uniform spinal core-   14 tubular arms-   16 shear wings-   17 disc-shaped bracing rings-   18 circular flange plates-   20 foundation for wind tower-   22 wind tower turbine nacelle-   24 turbine blade-   26 cone-shaped bracing rings-   28 openings in the shear wings with pairs of circular flange plates    18 at the edge of each opening.-   30 open areas-   32 rigid brackets with pairs of circular flange plates 18-   34 fanned-out tubular arms 34 engaged at their bottom with    foundation 20 or pontoon 52-   36 optional horizontal tubes.-   40 post-tensioned cables-   42 foundation-   44 rock anchors which go through the foundation 42 or outside    foundation 46-   46 foundation-   48 fanning out of post tensioned cables 40-   50 tubular arms or post-tensioned cables with wider distance from    uniform spinal core 12 beyond a typical prior art tower-   52 submerged pontoon-   54 tie-down cables for submerged pontoon-   56 high water level-   58 low water level-   60 sea bed-   62 anchorage-   70 top circular flange plate-   72 bottom circular flange plate-   76 top circular flange plate-   78 shop-welded stiffeners-   80 cables bearing plate-   82 opening in flange plates-   84 bottom circular flange plate-   86 cable assembly-   90 prior art wind turbine tower-   91 proposed optional fanned out base section for tower 90-   P lateral force-   KL effective buckling length

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the bending moments in a free-standing tower of a uniformdiameter subjected to a lateral force P. The bending moments are thesame for a tapered-tube tower. The bending moment increases as the towergets taller, even under a constant force, and with it, the sway of thetower. The bending moments increase linearly with height, while the swayincreases even more rapidly at the height to the power of three. Sincetoday's tower core must resist the total bending moment and control thetower sway all on its own, the taller the tower the larger its size mustbecome, necessitating a larger diameter and a thicker tube. Also, as thetower diameter increases, so must its shell thickness to prevent localbuckling. As a result, today's tower structure becomes considerably morecostly and significantly more difficult to fabricate, transport, andinstall. Transporting an oversized tower is subject to specialtransportation permits and in complex terrain or where physicalinfrastructure limitations exist, it is not possible to transport thetower on land at all.

The basic reduced profile wind turbine tower structure RPWTT 10supporting a turbine 22 with blades 24 (as shown in FIGS. 2 and 3) abovea foundation 20 uses the same footprint as the present tapered-tubetower 5. But instead of today's massive structure 5, the reduced profilewind turbine tower of the present invention RPWTT 10 utilizes a slimspine with strong arms (as shown in FIGS. 2 and 3). It employs asmaller, lighter, and uniform cylindrical spinal core 12 that can carryall needed utility lines and provide protected access to the nacelle atthe top of the tower. The reduced profile wind turbine tower core 12carries primarily gravity loads and resists shear and torsion. Itprovides the needed structural stability during construction andenhances the overall stability of the tower at each subsequent stage. Aseach level is installed, the tower gains strength and stability. Witheach completed level, a sturdy, stand-alone structure is created thatcan withstand forces and moments all on its own.

With a uniform, non-tapered, cylindrical spinal core 12, the splicing ofthe tower sections can employ full direct bearing of the upper towersection on its lower section and utilize shear splicing, eliminating theneed for the less efficient flange splices which require fullpenetration welds and subject the bolts and the full penetration weldsto tension. This can be accomplished by fitting a cylindrical pieceshop-bolted to the core's lower section and field-bolted to its nextupper section.

In reduced profile wind turbine tower RPWTT 10, only a small part of theexternal bending moments is resisted by the slim cylindrical spinal core12. The larger part of the bending moments is resisted by the highlyefficient, axially loaded tubular arms 14 interacting with the towercore 12 via continuous shear wings 16. Unlike today's tapered-tube tower5, the reduced profile wind turbine tower tubular arms 14 are uniformlystressed. They can be set vertically or slightly sloped. The arms 14 arelaterally braced by the spinal core 12 utilizing disc-shaped bracingrings 17 (as shown in FIG. 3) or more aerodynamic cone-shaped bracingrings 26 (as shown in FIG. 4). The latter bracing is also the solutionwhere nesting is a concern. In so doing, the presence of slendercomponents within the transformed tower structure is avoided. Globalstability is provided by the transformed structural system with thespinal core 12, the shear wings 16, and the tubular arms 14 acting inunison. The foundation design depends primarily on the specific reducedprofile wind turbine tower system used, the loads imposed on the tower,and the local geotechnical conditions. Connections between the reducedprofile wind turbine tower components are simple and can be detailed tobe shop-welded and field-bolted to facilitate fabrication and erectionmost efficiently.

One of the inherent drawbacks of today's prior art tower 5 results fromits structural system resisting the overturning moments through bendingonly. A cylindrical or tapered-tube tower is very efficient in resistingbuckling and torsion, but not very effective in resisting bending orlimiting sway, two key drivers in the design of a wind tower. In acylindrical or tapered-tube tower, bending under working conditionsproduces a gradient of internal stresses where only the extreme fiber ina tower's cross-section is stressed to the full strength of thematerial, leaving most of the tower's material under-stressed (as shownin FIG. 5). Consequently, under working conditions, most of today'stower material, when subjected to bending, is underutilized. The tallerand larger today's tower 5 becomes, the greater its materialunderutilization, and the greater the inefficiency in its structuralsystem.

The reduced profile wind turbine tower RPWTT 10 of the present inventionresolves this limitation by significantly reducing the bending momentson the cylindrical core 12 and employing it primarily in resistinggravity loads, shear, torsion, and buckling, where it is most suited.

Furthermore, the shear wings 16 can be designed with openings 28 tofurther simplify fabrication and erection and cut costs (as shown inFIG. 6). At the limit, most of the wing area may be left open, reducingthe shear wings 16 to rigid brackets 32 (or rigid cantilevers) placed atdistinct levels (as shown in FIG. 7). The brackets 32 are made ofvertical shear plates and horizontal circular flange plates 18. Thebracket assembly will be enclosed, as shown in FIG. 7A, to improveaerodynamics and prevent nesting. To keep the inside of the tower core12 mostly open, a stronger transition core section at the brackets 32may be required. This can be accomplished locally by utilizing asomewhat thicker core, while keeping the outside diameter of core 12unchanged. An added benefit of the rigid brackets 32 with their circularflange plates 18 (as shown in FIG. 7) is that they provide sturdyplatforms that can be used to erect the next tower level as well asfacilitate the installation of the turbine 22 and blades 24. In otherwords, in addition to their structural function in the tower RPWTT 10,they are capable of serving as a stage to support a climbing tower craneavoiding the need for a larger and much costlier land-staged crane.

Where project conditions permit, the tubular arms 14 can be fanned-outat 34 to reduce the anchoring forces into the foundation and, thereby,the anchorages themselves (as shown in FIG. 8). At the lower end of thetubular arms 14, the horizontal force component may be transferred tothe foundation or, optionally, this force may be transferred back to thetower core via a horizontal tube 36 (as shown in FIG. 8). In this way,the present invention “cancels-out” the horizontal force componentcreated in the tower core 12 by the fanned-out tubular arms 34 at theirupper end, thereby eliminating the need to account for the horizontalforce component in the connection between the core and the foundation,as well as that between the tubular arms 34 and the foundation 20.

In another transformation of the tower design, post-tensioned cables 40can be used to replace the tubular arms 14 (as shown in FIG. 9). Thecables 40 are post-tensioned to ensure that they remain with the propertension under all design loading conditions. Post-tensioning increasesthe compression force in the core 12. On the other hand, in utilizingcables, field connections are reduced and the fabrication,transportation, and erection streamlined. In fact, transportationbecomes a non-issue as shipping cables is a fairly standard truckingjob. Cables 40 can be shaped to follow any contour to meet the designneeds and choice. An added benefit of the post-tensioning is that, ineffect, it load-tests the tower system during construction. Moreover,the cables 40 can be anchored directly into the foundation 20, furthersimplifying construction operations. The cables 40 are designed to berestressable and replaceable. The reduced profile wind turbine towercables 40 can be braced at each bracket level with rigid brackets 32,making their unbraced length much shorter than the typical cables in usein bridges.

The tower core 12 can take various forms and it can be constructed ofdifferent materials such as steel, precast concrete, cast-in-placereinforced concrete, or post-tensioned concrete. Post-tensioning thereduced profile wind turbine tower cables 40 introduces compression intothe tower core 12 which reduces the moment-induced tension in the corestructure, thereby allowing for simpler and smaller splice connections.The post-tensioning of the cables 40 has an added benefit in concretestructures as it reduces the tension in the tower core 12, therebyrequiring less reinforcement and/or lesser internal post-tensioning. Inaddition, for efficiency, a slip form can be utilized to cast-in-placethe tower's uniform spinal core 12.

If necessary, the cables 40 can be protected locally at grade level byplacing each cable inside a protective casing approximately 20 to 25feet high from ground level. Depending on the security type desired, thespace between the casing and the cable can be grouted or a blastprotective jacket can be installed. The complete assembly will then besealed. Such a system was pioneered by the inventor in 1995, while aprincipal at another firm, and subsequently successfully implemented atseveral suspension bridges including the George Washington Bridge, theVerrazano-Narrows Bridge, and the Whitestone Bridge.

In competent rock substrate, the cables 40 can be anchored into the rockdirectly by rock anchors 44, reducing the size of the foundationsignificantly (as shown in FIG. 10). Furthermore, similar to a reducedprofile wind turbine tower RPWTT 10 with tubular arms 14 (as in FIGS.2-4 and 6-8), a reduced profile wind turbine tower RPWTT 10 withpost-tensioned cables 40 can have the cables 40 optionally fanned-out atlower cable portions 48 to substantially reduce the anchoring forces andthe size of the anchorages and foundation (as shown in FIG. 11).

Unlike today's tower 5, where increasing its capacity to resist externalbending moments and to control its sway necessitates a tower of a largerdiameter and/or a thicker shell at added costs, the reduced profile windturbine tower RPWTT 10 offers increased stiffness and capacity at lowercosts by widening the distance between the tubular arms or cables 50 andenhancing the tower efficiency (as shown in FIG. 12). In so doing, theaxial forces in the tubular arms or cables 50 and the shear forces inthe rigid brackets 32 are reduced, while the bending moment resisted bythe brackets 32 remains practically the same. This makes the modularreduced profile wind turbine tower designs possible for a range ofreduced profile wind turbine tower sizes, as the user can keep aconstant core size and only widen the distance between the tower'stubular arms or cables 50, subject to constraints imposed by the windturbine 22 and blades 24.

For tall towers, employing other arrangements of the tubular arms orcables 50 may be favored. FIG. 13, for example, shows a hexagonplan-arrangement of six tubular arms or cables 50. Such spread-outarrangements would be preferred in order to reduce the forces in eacharm or cable 50, thereby reducing the size of the arms or cables 50, thesize of the brackets 32, and the size of the transition core section atthe brackets 32. The number of levels of rigid brackets 32 may also beincreased to further reduce the forces in the tubular arms or cables 50and the bending moments in the spinal core 12, in order to reach awell-balanced solution.

The reduced profile wind turbine tower design of the present inventionproduces two interdependent subsystems: one is the uniform tower core 12(the core subsystem) and the other comprises the tubular arms or cables50 and their respective rigid brackets 32 with pairs of circular flangeplates 18 (the brackets subsystem). These two subsystems jointly resistthe external forces and moments, limit the sway of the tower RPWTT 10,and govern the overall stability of the tower 10. This presents thedesigner with the choice of determining how these two subsystems shouldshare in the overall design. Generally, the relative stiffness of thetwo subsystems drives the overall performance of the tower RPWTT 10. Arelatively soft tower core 12 would yield control to a stiff bracketsubsystem, while a relatively soft bracket subsystem would yield controlto a rigid tower core 12.

The interaction between the two subsystems presents us with a tool thatallows the designer to modify the tower structural behavior to meetproject-specific needs. Rather than a single free-standing tapered tubetower system 5, the user now has unlimited possibilities to mold andshape the tower RPWTT 10 structural system to his or her advantage. Thereduced profile wind turbine tower innovation transforms the designentirely from one in which the designer merely has a reactive role, toone in which, to a large extent, the designer is in command. The usermay explore related flexibilities in the design of the power generatingsystem, for example, in finding ways to increase the tower moment armwithout compromising the efficiency of the turbine 22 and blades 24.This can unlock a treasure-trove of new possibilities for optimizing thestructural design and the design of the wind power generating system asa whole, thereby unlocking previously untapped potential for reducingtotal expenditures and lowering the unit cost of energy.

The reduced profile wind turbine tower RPWTT 10 of the present inventionoffers many design options from which the user may choose the mostefficient alternative for a given set of conditions. The user may selecta different relative stiffness for the core 12 and bracket subsystems,different bracket plan arrangements, and different bracket levels. Forthe first design iteration, the user assumes that the tower core 12resists all shear forces and torsion, as well as the turbine and bladegravity loads, while the structure self-weight can be applied to eachstructural member individually. To reduce costs, the top section of theuniform core 12 is left to stand alone as a free-standing cantileverwithout the help of the bracket subsystem. This is possible since, inpractice, the uniform spinal core 12 itself has a certain inherentcapacity that is sufficient to resist the forces and moments on its own.In addition, the user assumes that the core 12 is subjected to completefixity at its base and to rotational fixity, in a vertical plane, ateach bracket level. The latter assumption is intended to minimize thecore size by assigning the larger portion of bending moments to the moreefficient moment-resisting bracket subsystem. This, in turn, translatesto a softer core 12 and a stiffer bracket subsystem. In subsequentiterations, the user fine-tunes the design to produce the most effectiveand economical overall system.

To demonstrate this approach, FIGS. 14 and 15 show a reduced profilewind turbine tower RPWTT 10 with a uniform core 12 and two bracketlevels, one at ⅖ height from the bottom of the tower and another at ⅘height from the bottom of the tower, where h is the tower overallheight. The top ⅕ height of the core is left to stand alone as afree-standing cantilever. FIG. 15 shows the bending moment diagram forthe core and the bracket subsystems under a lateral force P applied atthe top of the tower. This simplified assumption of a single force Pdoes not detract from the conclusions presented herein. In practice,instead of a single lateral force P, the user uses the actual lateralloads imposed on the tower RPWTT 10.

In this example, each bracket sub-system at each of the two levelsresists 40% of the total bending moment (as shown in FIG. 15). Thebending moment resisted by each bracket 32 is constant from thecorresponding bracket level down to the base of the tower at foundation20. Together, the brackets 32 at the two levels resist 80% of the totalbending moment imposed on the tower RPWTT 10. The core 12 resists only ⅕of the total bending moment, a mere 20%. This is five times smaller thanthe bending moment that would have been imposed on the core 12 had itbeen free-standing. In addition, it is noted that the bending moments inthe core 12 are not continuously increasing as in a free-standing tower(as shown in FIG. 1), but rather are re-distributed more evenly alongthe core 12, justifying the design of a uniform, more cost-effectivecore structure.

For the bending moment diagram shown in FIG. 15, the sway at the top ofthe core 12 is reduced 25 fold to a mere 4% of the sway of afree-standing core under the same conditions. Such a dramatic reductionin the sway of the tower has significant beneficial consequences inreducing the P-Δ effect in the tower design. Furthermore, the deformedshape of the core 12 is fundamentally altered, dropping the theoreticaleffective buckling length (KL) 5 fold, from KL=2 h for a free-standingcore to KL=(⅖) h in this case. Thus, the core in this case is able toresist significantly larger compression forces than a stand-alone coreof the same size. This example visibly demonstrates the beneficialinteraction between the two subsystems and illustrates the versatilityand structural potency of the reduced profile wind turbine tower design.

As the user introduces more bracket 32 levels along the tower RPWTT 10,the core 12 bending moments and the tower sway can be reduced evenfurther. This process, however, would not have to continue indefinitelyeven for tall towers, as a few bracket 32 levels would be sufficient toproduce an optimal solution. In practice, the user locates the bracket32 levels to coincide with the maximum transportable length of the towercore 12.

As noted earlier, in reduced profile wind turbine tower, the degree offixity between the core 12 and the bracket subsystem is determined bythe designer. An important variable in this relationship is the ratiobetween the stiffness of the tower core 12 to the stiffness of thebracket subsystem. The designer is presented with a trade-off betweenthe size of the tower core 12, the size of the tubular arms or cables50, the number of bracket levels, and the plan arrangement of thetubular arms or cables 50. The appropriate selection of these variables,to a large extent, depends upon the tower height, the forces imposed onthe tower RPWTT 10, the distance in plan between the tubular arms orcables 50 (moment arm), and the local soil conditions. The reducedprofile wind turbine tower RPWTT 10 affords the designer a powerful toolwith which he or she can control, mold, and shape the tower design.Through proper calibration of the reduced profile wind turbine towerdesign, the user can produce an efficient and cost-effectiveproject-specific tower structure RPWTT 10.

The cables 40 in a reduced profile wind turbine tower RPWTT 10 can beleft exposed, as they are when used in bridges. Similarly, the tubulararms 14 can be left exposed. Left exposed, this offers the smallestprojected surface area resisting the wind. However, if fornon-structural reasons it is desired to enclose the entire tower RPWTT10, the whole system can be easily tented utilizing lightweightreinforced fabric cladding, e.g. Teflon-coated woven fiberglass,attached to the cable system in a manner similar to tent-likestructures, either by attaching the fabric to the tower main cables 40or by introducing additional longitudinal cables to support the fabricenclosure independent of the main supporting structural cable system.The fabric is stretched taut over the cables to prevent slack andprovide the needed fabric stability under load. Tenting need not extendfrom the top of the tower RPWTT 10 to its foundation 20 if completeenclosure is not needed. Rather, it may terminate at any desired levelabove ground. Each bracket 32 with its pair of circular flange plates 18can serve as a natural termination point. Tents and other forms ofcable-supported fabric structures are a known and tested technology thatcan be integrated very well into the reduced profile wind turbine towerdesign. Currently, fabric structures offer a life span of about 30years.

The reduced profile wind turbine tower RPWTT 10 is a versatile andpowerful pioneering system that capitalizes upon the possibilities andbenefits offered by complete transformation of today's tower structure.The reduced profile wind turbine tower RPWTT 10 reverses today's tower 5limitations and enhances the performance and efficiency of the new towerRPWTT 10 system. With a reduced profile wind turbine tower RPWTT 10, thesway of the tower RPWTT 10 is effectively controlled, and the bendingmoments resisted by the tower core 12 become considerably smaller andmore evenly distributed along its height. The results unlock newpossibilities for taller, slimmer, and more cost-effective wind towersRPWTT 10 that can help reduce the capital costs of wind powerinstallations and aid in making wind power a more competitive form ofenergy.

The Offshore Solution: Floating

According to Navigant 2013, wind tower support, foundations, logisticsand installation account for 47% of offshore installation capital cost,without construction financing.

The DOE reports:

Almost all offshore wind installations have used a monopole or concretegravity base foundation in water less than 20 meters (65 feet) deep.Foundations for large offshore wind structures installed in deeperwater, whether fixed to the sea floor or floating, are one of the keyissues that will impact the feasibility of wind development attransitional depths. (U.S. Department of Energy Wind Energy MultiyearProgram, Plan for 2007-2012). The design, versatility, and simplicity ofthe reduced profile wind turbine tower make it an effective andeconomical system in offshore applications, as well. The reduced profilewind turbine tower is seamlessly adaptable to a floating tower byintegrating into its structural system the water's limitless power touplift. Floating bridges and structures, such as pontoons, have beenknown since Biblical times. Nonetheless, while water can provide aneconomical floating foundation, it introduces new challenges in the formof hydrodynamic forces, bobbing, sway, twist, and seesaw movements whichneed to be controlled in wind tower applications. The proposed floatingreduced profile wind turbine tower system responds to these challengesin a most effective way.

FIG. 16 shows a floating reduced profile wind turbine tower employing auniform spinal core 12, fanned-out post-tensioned cables 48, tie-downcables 54 and fully submerged pontoon 52. The pontoon 52 remains belowthe lowest expected water level 58 at all times. It provides apredetermined upward force designed to resist all gravity forces whilesimultaneously supplying the means against which the tower tie-downcables 54 are deliberately tensioned. This way, the user introduces aset uplift force that is independent of the actual water level andensures that the tie-down cables 54 remain in proper tension under alldesign loading conditions, independent of the water level. This alsoreduces cable fatigue and minimizes the effect of wave forces on thetower structure. The pontoon 52 can take different forms and beconstructed of different materials. The tie-down cables 54 are anchoredinto the seabed utilizing counterweights or soil anchorages. Thepost-tensioned cables 40 are fanned-out at 48 to reduce the forces inthem and permit an efficient taller tower to extend deeper into thewater and, in so doing, reducing the length of the tie-down cables 54.Reducing the length of the tie-down cables 54 is essential in making thefloating tower effective, as long tie-down cables 54 can adverselyaffect the sway at the top of the tower and, in turn, the towerperformance as a whole.

Tie-down cables 54 have been used effectively in floating structures formany years. Tension Leg Platforms (TLPs) utilizing vertical tie-downcables have been employed in floating oil rig construction for almostthree decades. However, unlike most floating structures, which typicallyare low-rise, heavy, with a comparatively wide base, and are subjectedto relatively small overturning moments, a wind tower is, in essence, ahigh-rise structure with a relatively light weight and narrow base andis subjected to substantial overturning moments. Consequently, theexternal overturning moments at the tower base translate into largeaxial forces in the tie-down cables 54, leading to considerableelongation and shortening of these cables that cannot be ignored in windtower applications. As water depth increases, the length of the tie-downcables 54, which hold down the tower and anchor it into the seabed,increases, as well. As a result, the differential elongation andshortening of these cables under external overturning moments increasesand, in turn, the sway at the top of the tower becomes significantlylarger.

With a pontoon 52 that is basically hinged in the water and with arelatively narrow tower base, the changes in tie-down cable length canbe magnified several-fold in the form of sway at the top of the windtower. Such large sway would adversely affect the tower performance.Large sway can also increase the overturning moments at the tower base,as the contribution of the tower gravity loads to the overturning momentin a swayed tower position becomes of substantial magnitude. The tallerthe tower, the narrower the horizontal distance between the tie-downcables 54, and the longer the tie-down cables 54 become, the moresignificant the effect of the tie-down cables 54 elongation andshortening on the sway at the top of the tower. To keep the cableelongation and shortening within acceptable limits, the diameter ofthese cables must become larger and/or the horizontal distance betweenthe tie-down cables 54 need to get wider. This solution, of course, hasits economical limits. An effective method to address this problem is toconstruct a taller tower and sink it deeper into water to shorten thelength of the tie-down cables 54. Although conventional towers usingtapered lattice or tapered tube structure 90 as in FIG. 16A can utilizethis new method, there is advantage to using this new method with thereduced profile towers of this invention. Unlike today's tower, where ataller tower requires a structure of a larger diameter at substantiallyhigher costs, a reduced profile wind turbine tower, by fanning out thetower post-tensioned cables 48 or tubular arms 34 below water, can bemade taller and sunk deeper into water at relatively minimal marginalextra costs.

The entire floating reduced profile wind turbine tower can bepre-assembled on shore, then floated and towed fully assembled togetherwith its pontoon 52 to its final destination offshore, where it would bepermanently anchored into the seabed. In this way, the massive andcostly monopole foundation, gravity base, or jacket structure used intoday's towers are completely eliminated.

FIGS. 17-20 show the details of alternate embodiments for fieldconnections at the bracket level for both tubular arm embodiments (asshown in FIGS. 17-18), as well as post-tensioned cable embodiments (asshown in FIGS. 19-20).

FIGS. 17 and 18 should be viewed together. These connections are shownas field welded, but they can be designed as field bolted, as well.Spinal core 12 is welded to both top circular flange plate 70, as wellas bottom circular flange plate 72. Tubular arms 14 are field welded tobottom circular flange plate 72, while cut pieces of the tubular arm areshop welded to bracket 32 and flange plates 70 and 72.

In corresponding views of FIGS. 19 and 20, top circular flange plate 76and bottom circular flange plate 84 are field welded to spinal core 12.Shop welded stiffeners 78 are welded to both top and bottom flangeplates and to bracket 32. Cable assemblies 86 go through openings 82 intop and bottom flange plates 76 and 84.

To summarize, this invention transforms today's single component tower5, into three general components: a spinal core 12, axially-loadedtubular arms 14, and shear wings 16 which join all three components towork as one unit in resisting the external forces and moments imposed onthe tower. The tubular arms 14 are braced by the spinal core throughbracing rings 17 or 26. In the reduced profile wind turbine tower 10 ofthe present invention, the spinal core 12 resists a small portion of theexternal moments, while the tubular arms resist the larger part of thesemoments. The tubular arms components are primarily axially-loaded. Asthe user introduces openings 28 in the shear wings, circular flangeplates 18 are added to reinforce the shear wings and to brace thetubular arms 14. As the user increases the size of the shear wingopenings, the shear wings are reduced to strong rigid brackets withpairs of circular flange plates 18, which together with the tubular armsform the bracket sub-system that resists the larger part of the externalmoments imposed on the tower. The system may be supported by afoundation on land or on a pontoon in water. In a general variation,post-tensioned cables 40 are used to replace the tubular arms 14. Boththe tubular arms and the post-tensioned cables work in a similar manner,interacting with the core 12 through rigid brackets 32 and their pairsof flange plates 18; the difference is that the cables must betensioned. The distance between the spinal core and the tubular arms orpost-tensioned cables may be enlarged to increase the efficiency of theresisting system of the reduced profile wind turbine tower 10 of thepresent invention. The spinal core, the bracket assembly, and thepontoon, may be constructed from any material that can resist the forcesand moments imposed on them. While tubes are shown herein for thetubular arms, the tubular arms can be constructed of anystandard-profile-cross-section.

CONCLUSION

The reduced profile wind turbine tower RPWTT 10 is a versatile andstructurally potent pioneering system that reverses today's towerlimitations, presents superior performance and offers significantadvantages that translate into exceptionally efficient andcost-effective wind towers. The reduced profile wind turbine tower RPWTT10 innovation completely transforms today's wind tower and unlocks newpossibilities for taller and slimmer wind towers that are easier andfaster to fabricate, transport, and install.

The reduced profile wind turbine tower system offers many advantages inthe fabrication and erection of wind towers. Actual cost savings fromutilizing the reduced profile wind turbine tower system depends on theproject-specific situation, geotechnical conditions, and the specificreduced profile wind turbine tower system employed. With a uniform andsmaller tower core, the fabrication and erection of reduced profile windturbine tower can advance faster and at lower costs. There are fewerconnections and a smaller number of tower core segments to be handledand put together. Accordingly, fitting, welding, bolting, monitoring,and testing are considerably reduced. In addition, steel plate rolling,cutting and waste, as well as surface preparation and painting of thetower, are dramatically cut. With pre-compression introduced into thetower core 12 by the post-tensioned cables 40, the tower core 12 can beconstructed of pipe sections bearing on one another and confined byexternal and internal rings, thereby simplifying installation andreducing construction time. The core 12 can be constructed of suitablestructural materials, such as, for example, steel or concrete—precastconcrete, cast-in-place, or post-tensioned concrete or a hybrid thereof.The slimmer and lighter reduced profile wind turbine tower core 12resolves the transportation limitations of today's tower and requires asmaller and less costly crane for erection. In addition, the brackets 32with their circular flange plates 18 are able to provide a sturdy stageto support a climbing tower crane to erect the next tower level, as wellas facilitate the installation of the turbine 22 and blades 24, therebyavoiding the need for a larger and much costlier land-staged crane.

The slimmer profile of the reduced profile wind turbine tower RPWTT 10diminishes the visual impact of today's wind towers. This is animportant advantage that can ease objections from environmental groupsto offshore wind farms and allow the construction of wind towers closerto shore. Given its slimmer profile, the new tower 10 would “disappear”from view faster than any other tower installed to date. All knownfloating wind towers use today's land-based tapered-tube structure andattempt to float and stabilize it in the water. No known structuralsystem has sought to float a wind tower and at the same time produce aslimmer, non-tapered tower with effective control of its movement. Thefloating reduced profile wind turbine tower completely eliminates themassive and costly monopole foundation, gravity base, or jacketstructure used in today's tower installations. As shown, a floatingreduced profile wind turbine tower can be pre-assembled on shore, thenfloated and towed fully assembled to its final destination offshore.

Today's prior art tower 5 offers only a single structural solution: afree-standing cantilever restrained at its base. As a result, today,optimization of the wind power system cannot be performed on the windpower system as a whole. In sharp contrast, the reduced profile windturbine tower RPWTT 10 design allows for the numerous variations oftowers and permits several variables to interact in optimizing theentire wind power generating system to include the tower structure 10,turbine 22, and blades 24. In this way, the reduced profile wind turbinetower RPWTT 10 unlocks previously untapped potential for reducing totalexpenditures and lowering the unit cost of energy.

The reduced profile wind turbine tower RPWTT 10 innovation permitseconomical and efficient super tall wind towers capable of harnessingmore powerful winds at higher altitudes, thereby advancing wind energyprojects far beyond their current limitations. It transforms wind power,both land-based and offshore, into a less expensive resource and offersnew possibilities for efficiently harnessing the abundant wind energyonshore, offshore, and further out at sea. The distinctive,wide-ranging, and vital advantages outlined herein present a majorbreakthrough that will indeed propel reduced profile wind turbine towerRPWTT 10 to become the tower of choice for the future.

It is to be understood that the aforementioned drawings and descriptionare merely illustrative of the present invention, and that nolimitations are intended to the detail of construction or design hereinshown, other than as defined in the appended claims.

I claim:
 1. A reduced profile wind turbine tower comprising: saidreduced profile wind turbine tower having a foundation adapted to beeither mounted in ground (20, 42, 46) or immersed in water (52); auniform outside diameter non-tapered cylindrical spinal core (12)supported directly on said foundation and extending up verticallydirectly from said foundation; a nacelle (22) mounted on a top end ofsaid uniform outside diameter non-tapered cylindrical spinal core (12);wind turbine blades (24) extending out from said nacelle (22); saiduniform outside diameter non-tapered cylindrical spinal core carryingall needed utility lines from said nacelle and providing protectedaccess inside said uniform outside diameter non-tapered cylindricalspinal core; and tubular arms (14) supported by and extending updirectly from said foundation distributed around and using spaced rigidbrackets (32) and pairs of spaced circular flange plates (18) extendingfrom said tubular arms over a length thereof for providing stiffness ofsaid tower and for reducing and modifying the bending moments imposed onsaid uniform outside diameter non-tapered cylindrical spinal core; saidtubular arms comprise a plurality of axially loaded tubular arms (14)surrounding said uniform outside diameter non-tapered cylindrical spinalcore (12) spaced therefrom, anchoring in said foundation (20, 42, 46)and extending up directly from said foundation (20, 42, 46) eithervertically or sloped and terminating substantially adjacent said nacelle(22) to resist both tension and compression forces imposed thereon andto substantially reduce the bending moments on said uniform outsidediameter non-tapered cylindrical spinal core (12); said spaced rigidbrackets (32) and said pairs of spaced circular flange plates (18)extending out from said uniform outside diameter non-tapered cylindricalspinal core (12); and said pairs of spaced circular flange plates (18)provide lateral bracing of said plurality of axially loaded tubular arms(14), wherein said spaced rigid brackets (32) and said pairs of spacedcircular flange plates (18) engage the plurality of axially loadedtubular arms (14) and provide a stage for a climbing crane to facilitatethe erection of the uniform outside diameter non-tapered cylindricalspinal core (12), the nacelle (22) and the wind turbine blades (24); inwhich said plurality of axially loaded tubular arms (14) are fanned-outat their lower portions for reducing anchoring forces into saidfoundation (20, 42, 46).
 2. The tower of claim 1 wherein said reducedprofile wind turbine tower is enclosed, at least partially, by a tauttenting sheath.
 3. The tower of claim 1 wherein said tower is made ofmaterials selected from the group consisting of steel, cast-in-placeconcrete, pre-cast concrete, post-tensioned concrete, or a hybridthereof.
 4. The tower of claim 1 wherein horizontal tubes (36) areprovided to join lower ends of said plurality of axially loaded tubulararms (14) for cancelling out horizontal force components created byfanned-out portions of said plurality of axially loaded tubular arms(14).
 5. A reduced profile wind turbine tower comprising: said reducedprofile wind turbine tower having a foundation adapted to be immersed inwater (52); a uniform outside diameter non-tapered cylindrical spinalcore (12) supported directly on said foundation and extending upvertically directly from said foundation; a nacelle (22) mounted on atop end of said uniform outside diameter non-tapered cylindrical spinalcore (12); wind turbine blades (24) extending out from said nacelle(22); said uniform outside diameter non-tapered cylindrical spinal corecarrying all needed utility lines from said nacelle and providingprotected access inside said uniform outside diameter non-taperedcylindrical spinal core; and tubular arms (14) supported by andextending up directly from said foundation distributed around and usingspaced rigid brackets (32) and pairs of spaced circular flange plates(18) extending from said tubular arms over a length thereof forproviding stiffness of said tower and for reducing and modifying thebending moments imposed on said uniform outside diameter non-taperedcylindrical spinal core; said foundation of said wind turbine tower is apontoon (52) being submerged in a body of water; said uniform outsidediameter non-tapered cylindrical spinal core (12) extending upvertically from the submerged pontoon (52); said submerged pontoon (52)being arranged for being anchored by tie-down cables (54), said tie-downcables (54) are arranged for being anchored at or into a seabed (60);said tubular arms comprising a plurality of axially loaded tubular arms(14) surrounding said uniform outside diameter non-tapered cylindricalspinal core (12) spaced therefrom, anchoring in said submerged pontoon(52) and extending up from said submerged pontoon (52) either verticallyor sloped and terminating substantially adjacent said nacelle (22) toresist both tension and compression forces imposed thereon and tosubstantially reduce the bending moments on said uniform outsidediameter non-tapered cylindrical spinal core (12); said spaced rigidbrackets (32) and pairs of spaced circular flange plates (18) extendingout from said uniform outside diameter non-tapered cylindrical spinalcore (12), wherein said pairs of spaced circular flange plates (18)provide lateral bracing of said plurality of axially loaded tubular arms(14), wherein said spaced rigid brackets (32) and pairs of spacedcircular flange plates (18) engage the plurality of axially loadedtubular arms (14) and provide a stage for a climbing crane to facilitatethe erection of the uniform outside diameter non-tapered cylindricalspinal core (12), the nacelle (22) and the wind turbine blades (24); andwherein the plurality of axially loaded tubular arms (14) are fanned-outat their lower portions for reducing anchoring forces into saidsubmerged pontoon (52).
 6. The tower of claim 5 wherein said tower isenclosed, at least partially, by a taut tenting sheath.
 7. The tower ofclaim 5 wherein said tower is made of materials selected from the groupconsisting of steel, cast-in-place concrete, pre-cast concrete,post-tensioned concrete, or a hybrid thereof.
 8. The tower of claim 5wherein horizontal tubes (36) are provided to join lower ends of saidplurality of axially loaded tubular arms (14) for cancelling outhorizontal force components created by fanned-out portions of saidplurality of axially loaded tubular arms (14).